The present invention relates to a novel side-chain liquid crystalline polymer having a temperature-dependent switchable tack property.
Tackiness is the ability of the surface of a material to adhere instantaneously to the surface of another material when the two materials are brought into contact with each other under a light applied pressure.
The preparation of conventional adhesives has been relied mainly on macroscopic and bulk techniques, i.e., blending various polymers and additives. However, such materials are not suitable for forming engineered interfaces which require special properties at specific processing conditions. For example, adhesives used in semiconductor dicing or grinding process, or in some biomedical processes, require switchable tackiness, an adhesive property that changes reversibly with the change of temperature, pressure or pH within a narrow range. In order to obtain an adhesive having such switchable tackiness, the molecular structure of the adhesive has to be designed to confer specific surface and viscoelastic properties thereon.
A side-chain liquid crystalline polymer undergoes a dramatic change from a highly structured state to a disordered state at its isotropic transition temperature and such a change over a narrow temperature range results in an abrupt change in its viscoelastic properties. Further, the surface properties of such a polymer would also undergo a sharp change at around the transition temperature, when the side chain and main chain thereof have different physicochemical characteristics relevant to the surface energy, unlike a conventional adhesive polymer whose viscoelastic property changes gradually over a broad temperature range.
Accordingly, the present inventors have endeavored to develop an adhesive polymer having tack properties that change sharply at a narrow temperature range.
It is, therefore, an object of the present invention to provide a side-chain liquid crystalline polymer which exhibits switchable tackiness at a narrow temperature range.
In accordance with one aspect of the present invention, there is provided a polymer of formula (I): 
wherein,
R1 is 
R2 is selected from the group consisting of xe2x80x94SO2xe2x80x94, xe2x80x94C(O)xe2x80x94, xe2x80x94CH(COOH)xe2x80x94, xe2x80x94C(COOH)2xe2x80x94, xe2x80x94C(S)xe2x80x94 and xe2x80x94C(NH)xe2x80x94;
R3 is xe2x80x94CH2xe2x80x94 or xe2x80x94CF2xe2x80x94;
R4 is H or F;
a is an integer ranging from 30 to 500;
b is an integer ranging from 1 to 3; and
c is an integer ranging from 3 to 20.